1. Field of the invention
The present invention relates to an apparatus for charging containers with powder such as toner from a hopper by predetermined amounts. The apparatus is particularly adapted for use in an image forming apparatus.
2. Description of the Prior Art
In an image forming apparatus a toner is contained in a container of a portable type, taking the form of a bottle or a cylinder. To charge such containers with toner, the toner is packed by dropping into the containers by weight. However, this charging method is disadvantageous in that the toner is prevented from smoothly dropping into the container because (1) air is present in the container, and (2) the toner is admixed with the air in the container, thereby expanding its volume.
In order to solve these problems, a toner is dropped by weight into a container up to half of the volume of the container, and after the supplied toner is allowed to fully settle in the container, a subsequent dose of toner is given so as to fill the remaining half of volume with toner. In this way the conventional charging method requires two steps, thereby becoming a time consuming process.
The inventor has made an invention which is disclosed in Japanese Patent Laid-Open Publication 1-124503. According to this prior invention, a toner is densely packed into containers at a high speed on a simplified charging structure. The prior invention will be more particularly described by reference to FIGS. 10 and 11:
The charging apparatus illustrated in FIGS. 10 and 11 includes a low pressure chamber 71, a pressure reducer 72 for reducing the pressure in the chamber 71, and a pressure raiser 73 for raising the pressure in the chamber 71. The low pressure chamber 71 can be divided into an upper section 71a and a lower section 71b, and houses a container 1 having an inlet neck portion 2.
The low pressure chamber 71 houses a powder supplier 75, which includes a tapered nozzle 74 inserted into the inlet neck portion 2 and a toner hopper 79 connected to the nozzle 74. The toner hopper 79 includes a toner path 76, and is provided with an outlet port 79a connected to the nozzle 74 through a supply path 81 having a valve 82 such as a ball. The toner stored in the toner hopper 79 is caused to fall into the toner path 76 by a predetermined amount.
The container 1 is raised and lowered by a pneumatic cylinder 80, and when it is raised, the open end of the inlet neck portion 2 comes into contact with a packing or O-ring 77 fitted around the nozzle 74, thereby sealing the inlet neck portion 2.
In operation, the low pressure chamber 71 is divided into the upper section 71a and the lower section 71b, and the container 1 is placed in the lower section 71b. Then, the two sections 71a and 71b are in an airtight manner connected to each other. At this stage, the inlet neck portion 2 is away from the nozzle 74. The valve 82 is closed, and the low pressure chamber 71 is evacuated by the pressure reducer 72 until a desired low pressure is achieved. In this way the low pressure chamber 71 and the container 1 have the same low pressure. Then, the container 1 is raised by the pneumatic cylinder 80 until the inlet neck portion 2 of the container 1 comes into contact with the packing 77, thereby ensuring that the container 1 remains evacuated to a desired degree of vacuum. Under this condition, the valve 82 is opened so as to open the toner path 76, and simultaneously, the pressure in the low pressure chamber 71 surrounding the container 1 is increased by the pressure raiser 73. Thus, the predetermined quantity of powder is sucked into the container 1 through the toner path 76. The rise in the pressure in the low pressure chamber 71 results in equilibrium between the internal pressure and the external pressure surrounding the container 1, thereby protecting the container 1 from being broken owing to any imbalance of pressure.
Under this construction the powder in the powder supplier 75 rapidly falls into the container 1 which is kept at a vacuum, thereby ensuring that the powder does not mix with air and does not lose its substantial volume.
However, one disadvantage is that the powder sucked into the container 1 is likely to be excessively compacted because of the scarcity of air in the container 1. At the initial stage, when a relatively large difference between the pressure in the inner container 1 and that surrounding it within the low pressure chamber 75, the powder violently collides with the bottom of the inner container 1. This tends to solidify the powder into lumps. When the powder is toner for use in an image forming apparatus, the lumpy toner is fatal in that a choking problem is likely to occur in the supply of toner.
In FIG. 10, the toner stored in the hopper 79 is likely to disperse outside the hopper as indicated by the arrows X for the following reason:
The toner in the hopper 79 is rapidly sucked into the outlet port 79a but because of the constriction therein the air is compressed against the inside wall of the hopper 79, and drives part of the toner to burst upward as shown in FIG. 10. The dispersion outward reduces the quantity of toner to be packed into the container 1.
Furthermore, when the pressure in the container 1 is reduced to a vacuum, the toner is so violently sucked into the container 1 that it tends to disperse in the container 1 and deposit in a ringshaped gap between the outside surface of the nozzle 74 and the inside surface of the inlet neck portion 2 as shown in FIG. 11 where the reference numeral 6 denotes a toner deposit. The deposit 6 is likely to drop into subsequent fresh containers 1, and when the atmospheric pressure is introduced into the low pressure chamber 71, the deposit 6 is likely to be dispersed in the low pressure chamber 71 and stains its inside wall. When the low pressure chamber 71 is stained with toner, it is required to clean it off at times by suspending the toner charging operation, thereby consuming extra time.